A liquid crystal display (LCD) device includes an LCD panel and a backlight module. The backlight module includes a light emitting diode (LED) backlight driving circuit. A typical LED backlight driving circuit uses a boost circuit, as shown in FIG. 1. A 220 V city voltage (alternating voltage) is rectifies as an input voltage 24 V (direct voltage) by a transformer T and a bridge rectifier circuit (AC/DC). An LED constant current driving chip controls a metal-oxide-semiconductor field-effect transistor (MOSFET) Q that adjusts voltage to turn on/off, and an inductor L, which can store energy and release energy, provides a great direct voltage for an LED lightbar. An equation of an output voltage of the boost circuit is: Vo=Vin/(1−D) (D is a duty cycle of a driving signal of the MOSFET.
A range of voltage raised by the boost circuit is limited. Generally, the range of the voltage raised by the boost circuit is within 100 V. If the range of the voltage raised by the boost circuit needs to be increased, a boost device is added, such as adding the transformer, which increases cost.